1. Field of the Invention
The present invention relates to a time-matching system and a time-matching method, in particular, to a time-matching system and a time-matching method for wireless communication terminal devices.
2. Description of the Related Art
In a computer network, time-data can be obtained by connecting to an NTP (Network Time Protocol) server. Also., a mobile GPS (Global Positioning System) receiver can obtain time-data from a GPS satellite which provides the time-data (referred to as satellite time-data) as well as position-data. Such satellite time-data has higher accuracy than time-data provided by an NTP server. A terminal device with a GPS receiver (or a terminal device connected to a GPS receiver) can obtain satellite time-data, and hence a clock within the terminal device can be calibrated by reference to the satellite time-data. However, the satellite time-data can not be shared between the terminal device and terminal devices with no GPS receiver (or terminal devices not connected to a GPS receiver).
A technology is desired, with which time-data with high accuracy can be shared between a terminal device having the time-data and other terminal devices on a wireless communication network (for example, a wireless Local Area Network).
Japanese Laid Open Patent Application (JP-P-Heisei 10-145845) discloses a mobile communication system. The mobile communication system includes a plurality of base stations, each of which has a GPS receiver. Time-data included in GPS-data received by the GPS receiver is delayed to generate a delayed timing signal. Each base station synchronizes a call signal from a mobile communication device with the delayed timing signal. Therefore, the synchronization between the plurality of base stations is achieved without presetting the amount of time-delay for each base station.
Japanese Laid Open Patent Application (JP-P2000-278746A) discloses a communication system. According to the communication system, a communication device receives a GPS synchronization signal from a CDMA (Code Division Multiple Access) network, and transmits a synchronization signal to a PHS (Personal Handy-phone System) network in synchronization with the GPS synchronization signal. Then, the system clock in the PHS network is corrected based on the received synchronization signal.
Japanese Laid Open Patent Application (JP-P2002-156477A) discloses a time correcting system. The time correcting system connected to a network includes a communication device having a receiving unit and a transmitting unit. Here, the receiving unit receives time-data to which a reliability parameter is added. The communication device generates new time-data by adding a reliability parameter of its own to the received time-data having the reliability parameter. Then, the communication device transmits the new time-data via the above-mentioned network.
The communication device further includes a time generating unit, a time-data extracting unit, a time-data comparing unit and a time correcting unit. The time generating unit generates own time-data. The time-data extracting unit extracts time-data having a reliability parameter from the data received by the receiving unit. The time-data comparing unit compares the own time-data generated by the time generating unit with the time-data having the reliability parameter extracted by the time-data extracting unit. The time correcting unit controls the time generating unit based on the result of comparison provided by the time-data comparing unit.
An object of the time correcting system mentioned above is to adjust automatically the clock build in each communication device on the network without concentrating the load on a certain communication device.
Japanese Laid Open Patent Application (JP-P2000-314771A) discloses a GPS-based information system. The GPS-based information system is composed of a plurality of GPS-based information transmitting stations and a plurality of information receiving terminals. Each of the plurality of GPS-based information transmitting stations includes a GPS antenna, a GPS receiver and a transmitter.
The GPS antenna receives radio waves from GPS satellites. The GPS receiver receives GPS-data from the GPS antenna and outputs position-data and time-data to the transmitter. The transmitter transmits the position-data and the time-data to the plurality of information receiving terminals.
An object of the GPS-based information system mentioned above is to reduce the electrical power consumption of each terminal by reducing the amount of calculation for detecting its location. Another object is to manage the users' security and locations by utilizing the wireless LAN communication.